The invention relates to new transparent, photochromic and non-photochromic organic materials, which have a high refractive index with no optical distortion in the mass, to a process for their preparation, and to articles formed from these materials.
The production of a photochromic ophthalmic lens made of plastic material is very difficult. Ideally, the polymer matrix of such a lens should be thermally crosslinked, should be free of optical distortion in the mass, and should be capable of receiving and of being crosslinked in the presence of appropriate mixtures of photochromic coloring agents, such as spiroxazines and chromenes, in order to obtain a material with a high initial transmission before exposure and an extensive darkening capacity after exposure, all this with rapid darkening and lightening kinetics. Moreover, the material should have a low thermal dependence, a high fatigue strength, and a high refractive index.
Several materials have been suggested for making such materials. For example, WO-A-92/05209 describes a copolymer, which is free of optical distortions, which is suitable for manufacturing glasses for eyeglasses, which is obtained by radical polymerization of a first monomer having the following formula: ##STR4##
in which a and b are whole numbers from 0 to 4, R.sub.1 and R.sub.2.dbd.H or CH.sub.3, and R.sub.3.dbd.--O--, --S--, --CO--, --SO.sub.2 --, --CH.sub.2 --, --CH.dbd.CH-- or CH.sub.3 --C--CH.sub.3, with a second monomer which can be styrene or a styrene derivative, and optionally, a third monomer which can be an aromatic vinyl compound or an aromatic methacrylate, in the presence of an initiator of the peroxide type and a chain transfer agent chosen from various brominated compounds. While the copolymer of the above reference may provide a polymer matrix for a photochromic article, such as a lens, attempts to incorporate photochromic coloring agents in the copolymerizable composition failed because the coloring agents tend to be destroyed by the peroxide initiator. And even if the peroxide initiator is replaced by a gentler radical polymerization initiator, such as a diazoic compound such as azo-bis-isobutyronitrile, the material which is obtained is still unsatisfactory because the photochromic coloring agents are inhibited by the brominated chain transfer agent which is used, as the present inventors were able to observe.
One method which has been suggested for overcoming the above problems is to incorporate the coloring agents in the matrix after polymerization, for example, by a thermal diffusion process. However, such a process tends to be inefficient, adds to the manufacturing cost of the material and complicates its process of manufacturing.
In order to remedy the above problems, co-pending, co-assigned French Patent Application No. 95 08424, filed Jul. 12, 1995, for "New photochromic organic materials," (herein incorporated by reference), discloses a new transparent photochromic organic materials having a refractive index greater than 1.55 and free of optical distortions, obtained by radical polymerization of a polymerizable composition containing:
a) 80 to 95 wt % of at least one monomer represented by general formula (I): ##STR5## PA1 b) 5 to 20 wt % of at least one aromatic monovinyl monomer represented by general formula (II): PA1 where R.sub.1.dbd.H or CH.sub.3 ##STR6## PA1 c) optionally, up to 10 wt % of an aromatic divinyl monomer represented by the general formula (III): PA1 where R.sub.1.dbd.H or CH.sub.3. ##STR7## PA1 d) an effective quantity of at least one coloring agent giving the material photochromic properties, chosen from the group of the spiroxazines, spiropyrans and chromenes; PA1 e) an effective quantity of a chain transfer agent; and PA1 f) an effective quantity of a radical polymerization initiator; characterized by the fact that the chain transfer agent is a straight-chain alkanethiol, and the radical polymerization initiator is a diazoic compound, as well as a process for preparation of these photochromic materials and photochromic articles consisting of these materials. PA1 a) 50 to 90 and preferably 55 to 70 wt % of units derived from at least one monomer represented by general formula (I): ##STR8## PA1 b) 10 to 30 and preferably 15 to 25 wt % of units derived from at least one aromatic monovinyl monomer represented by general formula (II): PA1 where R.sub.1.dbd.H or CH.sub.3 ; ##STR9## PA1 c) up to 15 wt. %, preferably 2 to 6 wt. % of units derived from an aromatic divinyl monomer represented by general formula (III): PA1 where R.sub.1.dbd.H or CH.sub.3 ; ##STR10## PA1 d) 1 to 20 and preferably 5 to 15 wt % of units derived from at least one (meth)acrylic monomer corresponding to the general formula (IV): EQU CH.sub.2.dbd.C(R)--COOR' PA1 R' is a straight-chain or branched C.sub.4 to C.sub.16 alkyl radical, an alkylaryl radical, or a polyoxyethoxylated group with formula --(CH.sub.2 --CH.sub.2 O).sub.n R" in which n=1 to 10 and R".dbd.CH.sub.3 or C.sub.2 H.sub.5, and PA1 e) optionally, an effective quantity of at least one coloring agent giving desired photochromic properties, chosen from the group of the spiroxazines, spiropyrans and chromenes. PA1 Diacryl 121 of Akzo Chemical (DIA) PA1 Styrene (STY) PA1 Divinylbenzene (DVB) PA1 2-ethylhexyl methacrylate (AEH) PA1 Butyl methacrylate (MAB) PA1 Ethyltriglycol methacrylate (MAET) PA1 2-2' Azobis 2-methylbutyronitrile (AMBN) PA1 1-dodecanethiol (DDT) PA1 Red PNO, a spiroxazine marketed by the company Great Lakes.
in which R.dbd.H or CH.sub.3, and m and n are independently 1 or 2;
Although the photochromic materials described in the aforementioned French patent application represent a significant advance, there continues to be a need for organic materials which are easier and therefore less costly to form into lenses free of optical defects